-LRB- CNN -RRB- -- Marin Cilic made a winning return to the ATP circuit Monday after serving a reduced doping ban .

The 25-year-old Croatian completed a tight three set victory over Dutchman Igor Sijsling at the Paris Masters , prevailing 5-7 6-1 6-4 at Bercy Stadium .

Cilic has slipped to World No. 47 after testing positive for the stimulant nikethamide at the Munich Open in May .

He was banned for nine months by an independent tribunal in September , but his appeal to the Court of Arbitration for Sport saw his suspension cut to four months last Friday .

The decision allowed Cilic to enter the final regular season tournament on the main tour in the French capital and he took full advantage .

Despite losing the first set , Cilic earned a second round match against in form World No. 5 Juan Martin Del Potro of Argentina .

He later admitted that he was pleased to put the experience behind him and return to action .

`` I would definitely say it was the worst time of my life as a player , '' he told AFP .

`` I have been on the tour for six , seven years , and have been always really careful and really honest and fair as much as I could with all the other players .

`` And then to be in that kind of situation where when I found out about the positive test it was an extremely difficult situation where people were even calling me a doping player and a cheat .

`` I knew I did n't cheat , '' added Cilic .

World No. 1 Rafael Nadal , who is playing in Paris for the first time in four years , told gathered reporters that he was delighted to see Cilic return to action .

`` One thing I can say is I 'm happy to see Marin back on tour . He 's a good guy and a great player , '' he told AFP .

`` I do n't know what happened but if he 's back , it 's because it 's fair that he 's back . That 's all . I 'm happy for that . ''

Nadal will open his campaign later in week but the early headlines will surround players attempting to book their passages to the ATP World Tour Finals in London .

Roger Federer , Swiss colleague Stanislas Wawrinka and French duo Richard Gasquet and Jo-Wilfried Tsonga are battling for the final three places in the elite eight-man field , with four others having mathematical chances of qualifying .

Wawrinka learned his second round opponent in Paris as Spaniard Feliciano Lopez won a tight encounter against Australian qualifier Bernard Tomic 6-4 6-7 7-6 Monday .

Federer , who needs one win to clinch a 12th consecutive appearance in the finals , will face the winner of the first round match between Kevin Anderson and Mikhail Zouzhny , while Gasquet and Tsonga could meet in the third round of their home event .

World No. 2 Novak Djokovic claimed the ATP finale last season , beating Federer in the final , while Nadal has never claimed the title .

The Spaniard hopes to use a good performance in Paris as a springboard to success in London .

`` The last tournament of the year is important , '' he told the official ATP Tour website .

`` In 2010 I played well -LRB- lost in the final to Federer -RRB- ; the rest I played really bad . I want to try to change that .

`` I was always motivated for this last part of the season , but I was not able to apply it well . I hope this year I can change that situation . I hope to play well here and then we 'll see . ''

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Marin Cilic wins on return to ATP Tour after doping ban

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Court of Arbitration cut his suspension from nine to four months

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Cilic beats Igor Sijsling in first round of Paris Masters

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Rafael Nadal playng tournament for first time since 2009